As engine emissions requirements become stricter and horsepower ratings increase, aftercoolers on internal combustion engines are required to reject increased heat. The increased heat rejection and a high level of transient operation may cause thermal stress in the aftercoolers. When an engine is operated at a high load for any extended period of time, the aftercooler eventually reaches a steady state thermal condition characterized by a substantially constant temperature gradient through the depth of the aftercooler core. This temperature gradient, combined with the differences in Coefficient of Thermal Expansion (CTE) of the various materials within the core, induces stresses in the core. Changes in engine power and charge-air flow interrupt this balance resulting in a new temperature gradient and a new distribution of stress. A rapid change of the temperature within the core as the core adjusts to the new thermal conditions drives large changes in stress. An increased rate and magnitude of these thermal shock cycles may decrease the life of the aftercooler.
Reducing the overall temperature in which the aftercooler must work is effective in reducing stresses, but may negatively impact engine performance, or result in an increase in aftercooler size. Aftercoolers may also be produced with materials capable of withstanding the stresses inherent in their operation. While higher strength constituent materials are available, many aftercoolers have copper as one of their prime constituents due to its superior heat transfer properties. Many aftercoolers are assembled with a brazing process, a factor that compounds Copper's low mechanical strength. These braze joints are difficult to produce consistently and their fatigue characteristics (or behavior) are difficult to predict. Designing aftercoolers with the proper constraints such that changes in temperature and the corresponding thermal expansion do not set up resulting stresses may also be costly.
Aftercooler bypass circuits and flow control valves are known to those skilled in the art as a means to control the intake manifold air temperature for increased engine performance or reduced engine emissions, while providing the proper level of cooling for the engine block. For example, U.S. Pat. No. 4,697,551 to Larsen, et al, discloses a system with a proportional radiator shuttle valve to allow all or some of the engine coolant to flow through the radiator or alternatively through a radiator bypass flow conduit to the aftercooler. A quick-acting proportional aftercooler shuttle valve can allow mixing of cool coolant from the radiator which bypasses the aftercooler with coolant through the aftercooler.